Thisfield is evolving rapidly as new tools for capturing dietary intake are devel-
oping. In addition, advanced biomarkers of nutrient exposure, including metabo-
lomics, make possible the assessment of the metabolic end products of dietary
intake.
Dietary Measurement: Self-Report
The majority of studies on diet-related exposures rely on self-report of dietary
selections. While it is clear that measurement error is introduced when self-report
methods are employed (Natarajan et al. 2010 ), this methodology continues to be
common practice simply because it is somewhat valid at the population level, can
capture changes in dietary choices over time, has a reasonable level of participant
burden, and is cost-effective. The main dietary measurement methods used in
population studies are (1) food records or food diaries, (2) repeat 24-h recalls, and
(3) food frequency questionnaires (FFQ). Alternately, a diet history may be used in
which the respondent provides a single 24-h recall combined with an abbreviated
food list from an FFQ. Additionally, brief questionnaires that target specific nu-
trients (fat) or food groups (fruit and vegetables) have also been applied.
Food Records or Diaries
The food record or diary is a detailed, usually written account developed by the
respondent to record each and every food, beverage, condiment, or dietary sup-
plement consumed on a daily basis over a pre-specified period of time. To capture
habitual energy intake for an individual, a 31-day reporting period is considered the
minimum to achieve an acceptable level of accuracy (Basiotis et al. 1987 ). This
expands to 65 days for measurement of fat intake at the individual level. In order to
optimize reporting, the respondent must be trained in advance on the“how-tos”of
intake documentation including the importance of detail. Respondents list the item
consumed, any identifying brand information, qualification of preparation method,
and portion size. Portion size estimation is an important aspect of training and in
some circumstances respondents will be asked to weigh and measure all intakes. In
addition to recording food consumed, respondents commonly report time of day,
meal/snack, location when consumed and eating environment (e.g., with family,
friends). While, in general, recordings are made in writing, more recent advances in
mobile technology have moved this approach toward cell phone or Web applica-
tions (e.g., USDA Supertracker, My Fitness Pal).
Strengths of this approach lie in the detail of intake collected, real-time data
capture (versus recall), and the opportunity to evaluate eating patterns such as meal
frequency and timing, beyond nutrient intake alone. Weaknesses relate to the high
burden on respondents which frequently leads to missing data and the burden of
172 T.E. Crane and C.A. Thomson